Photodetectors are sensors for detecting electromagnetic waves or light. Often, photodetectors are quantum devices in which an individual photon produces a discrete effect. Photodetector applications vary according to electromagnetic wavelength, optical power, dynamic range, linearity, quantum efficiency, bandwidth, size, robustness, and cost. Photodetector types include chemical detectors such as photographic plates, photoresistors that change resistance if illuminated, photodiodes, and phototransistors.
Typically, a photodiode includes a photon detection region, such as the depletion region of a p-n junction, the intrinsic region of a p-i-n structure, or the absorption region of an avalanche diode. If light of sufficient energy strikes the photodiode, the light excites electrons thereby creating mobile electrons and positively charged electron holes. If absorption of the light occurs in the photon detection region or one diffusion length away from it, carriers are swept from the photo detection region to produce photocurrent. This photocurrent is a reverse diode current that varies linearly with illumination above the dark current region. Photodiodes can be operated under zero bias in photovoltaic mode or under reverse bias in photoconductive mode.
Some photodiodes are manufactured via planar metal oxide semiconductor field effect transistor (MOSFET) technologies. Typically, a photodiode is situated in its own active area, such as an n-doped well or an isolated silicon island/mesa having a different potential than the grounded substrate, which uses valuable real estate on the wafer. Manufacturing vertical photodiodes in planar MOSFET technologies increases the complexity of the MOSFET process, since an additional doping implantation step is needed to provide p-n junctions at different depths of the active area. In addition, planar MOSFET technologies may not be scalable beyond the 32 nanometer technology node.
For these and other reasons there is a need for the present invention.